A variety of catalysts, both homogeneous and heterogeneous, have been disclosed as oligomerization and dimerization catalysts for ethylene. For example, U.S. Pat. No. 4,482,640 and U.S. Pat. No. 4,487,847 disclose ethylene oligomerization and ethylene dimerization catalyst systems and processes. Efforts to raise the productivity and selectivity of ethylene dimerization and ethylene oligomerization catalysts and processes is ongoing due to the increasing importance of molecules having a molecular weight greater than ethylene.